The guy in front is a pro boxer.  He took up boxing because all the kids picked on him in school.  He found a way to let his anger out through boxing.  He is about to have a big fight the next night, and he is sitting there in front of the mirror, visualizing the next night in his mind.  The guy in the background is the image of his opponent.  His image is dark and shady, because he has been known to fight rough.  He is from the streets of Madrid, and grew up defending his life by fighting.  The guy in the picture is scared to face him but knows he has much more formal training.  The next night, the fight turns dirty.  One bad punch by the guy in the picture and his opponent grabs a knife and stabs him, killing the world's greatest boxer.
